The specific aims of the proposed research are as follows: 1. To investigate solvent-radical interactions of biological radicals; 2. To investigate biological semiquinones in rigid media; 3. To study the influence of hydrogen bonding on radicals at low temperatures. In order to investigate radical-solvent interactions of biological semiquinones, a simpler quinone, benzoquinone, was first studied. The benzosemiquinone anion radical was generated either chemically, photochemically or electrochemically in protic and aprotic solvents and then its esr spectrum was studied at temperatures from 300 to 4.2 K in order to determine the effect of the solvent on the semiquinone's spectrum. Power saturation studies were also performed. Quinone-lipid interactions were investigated using spin labeled stearic acid molecules. The lowest excited triplet state of various quinones was also studied at 77K in protic and aprotic solvent as well as oriented membrane multilayers.